A photomultiplier is a device that able to multiply by many times the photoelectrons produced by incident light. The photomultiplier thus may detect the incident light even when the incident light is very weak. The photomultiplier has important applications in nuclear and particle physics, astronomy, medical diagnostics including blood tests, medical imaging, motion picture film scanning, radar jamming, and high-end image scanners.
FIG. 1 schematically shows a conventional photomultiplier tube (PMT) 100 that includes a housing 101 containing a photocathode 102, several dynodes 104 and an electron collector 110. Light entering the PMT 100 and incident on the photocathode 102 causes photoelectrons to be emitted by the photocathode 102, as a consequence of the photoelectric effect. The photoelectrons emitted by the photocathode 102 may be referred to as primary electrons. The primary electrons impinge on the successive dynodes 104, causing electron multiplication by secondary emission. The electrons emitted from the dynodes 104 may be referred to as secondary electrons. On average, the amount of electrons emitted from each dynode 104 is greater than the amount of electrons impinging on that dynode 104. Secondary electrons emitted from the last dynode are collected by the collector 110 and used for detection of the incident light. Although being widely used, the PMT 100 is large in size, heavy, fragile, expensive and difficult to produce.